Air blast circuit breaker with damping resistor in parallel with the main breaking gap



Feb. 15, 1966 H FORWALD 3,235,695

AIR BLAST CIRCUIT BREAKER WITH DAMPING RESISTOR IN PARALLEL WITH THE MAIN BREAKING GAP Filed June 20, 1962 United States Patent 3,235,695 AIR BLAST CIRCUIT BREAKER WETH DAMPING RESISTOR IN PARALLEL WITH THE MAIN BREAKING GAP Haakon Forwald, Ludviira, Sweden, assignor to Allmanna Svenska Eiektrislra Aktieholaget, Vasteras, Sweden, a corporation of Sweden Filed .l'une 20, 1962, Ser. No. 203,792 Claims priority, application Sweden, June 26, 1961, 6,665/61 5 Claims. (Cl. 2%0-148) This invention relates to a novel construction for air blast circuit breakers having resistor means in parallel with the main breaking gap and more specifically relates to a novel housing arrangement wherein the resistor and the interrupting contacts are contained in separate chambers which are each adapted to contain high pressure air with a non-return valve connecting the interior of the interrupter chamber with the interior of the resistor chamher.

The provision of a resistor in parallel with the interru-pting contacts of an air blast circuit breaker is well known to the art. in such an application, during the operation of the interrupter, substantial current can flow through the resistor to cause substantial heating. By way of example, where the circuit breaker acts on a fault which is at a distance of the order of one kilometer from the circuit breaker, the resistor which operates as a damping resistor'may conduct a current of several thousand amperes for several half cycles. An auxiliary breaking gap which connects the resistor in the line to be protected is thereafter operated to completely open the circuit breaker.

The energy built up in the resistor during this time will generate considerable amounts of heat. Moreover, and because of the short time in which energy is generated, it may be assumed that the resistor material will have to absorb all of this energy before it begins to cool.

In making these resistors and in physically mounting them in the circuit breaker, materials are used which will withstand as high a temperature rise as possible and the resistor is preferably contained within a compressed air filled container which is normally the same container which carries the interrupting contacts.

Because of this construction, the air within the container will be heated to extremely high temperatures to thereby decrease dielectric strength of the air and thus jeopardize the interrupting ability of the circuit breaker.

The principle of the present invention is to provide a novel structure in which the interrupter contacts are contained in a first compressed air filled chamber while the resist-or is connected in a second compressed air filled chamber. In order to supply compressed air to the resistor chamber, a one-way valve is connected between the two chambers so that the resistor chamber can be supplied with air f-rom the interrupter chamber. However, because this valve is a one-way valve, when the compressed air within the resistor chamber is heated it cannot return to the interrupter chamber. Moreover, and as an unexpected advantage of the invention, since the air within the resistor chamber is confined in a small volume by virtue of the one-way valve arrangement, the pressure within the resistor chamber will. increase as the air is heated so that the dielectric properties within the resistor chamber will remain sutficiently high to prevent short circuiting of the resistor. Thus, the insulation within the resistor container presents no special difiiculties as the separate container for the resistor without greater costs may be made to withstand higher pressure than the other parts of the breaker.

Where desired, a safety valve or overpressure valve can 3,235,595 Patented Feb. 15, 1966 be provided in the resistor chamber to prevent the build up of pressures which could rupture the chamber. Furthcrmore, the resistor chamber can be formed of a metallic housing with suitable cooling fins to permit rapid dissipation of heat.

Accordingly, a primary object of this invention is to provide a novel interrupter structure in which the heating of a parallel connected resistor will not interfere with the dielectric integrity of the interrupter chamber.

Another object of this invention is to provide a novel duel housing arrangement for interrupter contacts and a parallel connected resistor respectively where the two are pneumatically connected through a non-return valve.

These and other objects of this invention will become apparent from the following description of the accompanying drawing which schematically illustrates, in cross-section, an air blast circuit breaker constructed in accordance with the invention.

Refer-ring now to the invention, the circuit breaker is mounted on a tank 16 which serves as a source of high pressure gas which can be supplied to tank 10 over the conduit 11. A hollow insulation post 12 extends from tank 10 and carries the interrupter structure 13 of the circuit breaker. This interrupter structure 13 is more specifically comprised of an interrupter chamber 14 and a resistor chamber 15.

The interrupter chamber is formed of a metallic enclosure 16 and has 2 insulator bushings 17 and 18 extending therein. The insulator bushing 17 is schematically illustrated as terminating in a movable auxiliary breaking contact 1? and stationary interrupting contact 20. The stationary main interrupting contact 20 cooperates with a movable interrupter contact 21 which is connected directly to the metallic wall 16 of the interrupter housing 14. Terminal bushing 18 is terminated with a stationary contact 22 which cooperates with auxiliary interrupter contact 19. The movable contacts 19 and 21 are operated in a predetermined sequence by appropriate operating mechanism-s (not shown) which do not form any part of the present invention.

The resistor chamber 15 carries a resistor means 16' therein which has one end connected to the upper end of terminal bushing 18 and its upper end is connected to the metallic walls 23 of resistor chamber 15. The metallic walls 23 are electrically connected to walls 16 of interrupter chamber 14 and can be provided with fins, such as fin 24, to serve as an aid in dissipating heat generated by resistor 16'.

A one-way valve 30 is then connected between conduit 31 which leads through wall 16 of interrupter chamber 14 and orifice 32 in the wall 23. The one-way valve 30 is so arranged that it will permit gas to flow from chamber 14 and into chamber 15 but will prevent flow of gas from chamber 15 to chamber 14.

An overpressure valve 33 may be provided for orifice 34 in housing 15 to prevent the rupture of the housing by excessively high pressures.

It will also be noted that the housing walls 23 of the housing 15 are preferably stronger than walls 16 since housing 23 will normally be exposed to higher pressures than will the walls 16 of housing 14.

In operation, the interior of tank 10 and thus the high pressure gas therein is connected to the interior of tank 14 so that the interrupter contacts are immersed in this high pressure gas. This same pressure exists within container 15 by virtue of the one-way valve 30. When the circuit breaker is in its closed position, contacts 19 and 22 are closed. When the circuit breaker is to be opened, the interrupter contacts 20 and 21 operate to clear the fault. Contacts 19 and 22 remain closed so that resistor 16' is connected in parallel with contacts 20 and 21. Under certain fault conditions the current fiow through resistor 16 which is initiated with the opening of contacts 26 and 21, can be extremely high and, for example, could be of the order of several thousand amperes. After a predetermined number of half cycles of this relatively high resistor current, the current through resistor 16' is opened by the disconnection of contacts 19 and 22. However, during the predetermined number of half cycles of relatively heavy resistor current flow through resistor 16, a considerable amount of heat is generated in the resistor 16.

This heat, however, in accordance with the present invention will not adversely alTect the temperature of the air within chamber 14 since the heated air is confined to the chamber 15, the one-Way valve 30 preventing the flow of air from chamber 15 t0 chamber 14. At the same time, air pressure within chamber 15 which has a relatively small volume compared to the volume of chamber 14 will increase due to the increase in temperature to permit maintenance of the dielectric strength of the air within chamber Thus, the insulation within the resistor chamber 15 is not adversely decreased because of the increase of the temperature.

So that the pressure chamber 15 cannot rise to too high a value which could cause structural damage, the overpressure valve 33 is adjusted to relieve pressure when it reaches a predetermined high value.

Although I have described preferred embodiments of my novel invention, many variations and modifications will now be obvious to those skilled in the art, and I prefer, therefore, to be limited not by the specific disclosure herein but only by the appended claims.

I claim:

1. An air blast circuit breaker comprising means forming an interrupter chamber and a resistor chamber each containing a high pressure gas, a resistor means contained within said resistor chamber, a main interrupting contact means and an auxiliary interrupting ,contact means contained within said interrupter chamber, said resistor means being electrically connected in parallel ,.With said main interrupting contact means, said resistor means and said auxiliary interrupting contact means being electrically connected in series; non-return valve means pneumatically connecting said two chambers for permitting the flow of gas from said interrupter chamber to said resistor chamber while preventing the flow of gas from said resistor chamber to said interrupter chamber, said resistor means being exposed to the high pressure gas in said resistor chamber.

2. The device as substantially set forth in claim 1 wherein said resistor chamber can withstand pressure in excess of the pressure which can be withstood by said interrupter chamber.

3. The device as set forth in claim 1 wherein said resistor chamber is formed of metallic Walls having cooling flanges secured thereto.

4. The device as set forth in claim 1 wherein said resistor chamber includes pressure release valve means.

5. The device as set forth in claim 1 in which the interrupter chamber is located to one side of the resistor chamber.

References Cited by the Examiner UNITED STATES PATENTS 2,068,522 1/1937 Thordarson 200-166 2,160,660 5/1939 Hobart 200148 2,459,612 1/1949 Baker 200-148 2,729,721 1/1956 Forwald 20()-148 2,921,168 1/1960 Forwald 200-l48 2,981,815 4/1961 Leeds et al. 200l48 KATHLEEN H. CLAFFY, Primary Examiner.

ROBERT K. SCHAEFER, BERNARD A. GILHEANY,

Examiners. 

1. AN AIR BLAST CIRCUIT BREAKER COMPRISING MEANS FORMING AN INTERRUPTER CHAMBER AND A RESISTOR CHAMBER EACH CONTAINING A HIGH PRESSURE GAS, A RESISTOR MEANS CONTAINED WITHIN SAID RESISTOR CHAMBER, A MAIN INTERRUPTING CONTACT MEANS AND AN AUXILIARY INTERRUPTING CONTACT MEANS CONTAINED WITHIN SAID INTERRUPTER CHAMBER, SAID RESISTOR MEANS BEING ELECTRICALLY CONNECTED IN PARALLEL WITH SAID MAIN INTERRUPTING CONTACT MEANS, SAID RESISTOR MEANS AND SAID AUXILIARY INTERRUPTING CONTACT MEANS BEING ELECTRICALLY CONNNECTED IN SERIES; NON-RETURN VALVE MEANS 